Showing papers on "Surface plasmon resonance published in 1988"

Surface–plasmon microscopy

Abstract: The imaging of low-contrast samples is a challenging task for optical measuring techniques, especially if high lateral resolution is also required. For example, a heterogeneously organized lipid monolayer transferred from the water surface to a solid substrate1 still needs an additional contrast enhancement mechanism (the solubility difference for a fluorescing chromophore incorporated between the fluid and the crystalline domains of the monolayer) to be visualized by fluorescence microscopy. The mere thickness or index contrast between the different regions is not sufficient to use either phase contrast or Nomarsky microscopy2 or the more recently developed Isoscope ellipsometer3. Here we describe a new microscope technique—surface plasmon microscopy (SPM)— which offers superior contrast without loss of spatial resolution by using plasmon surface polariton (PSP) fields instead of normal light as the illumination source. Such electromagnetic modes travel along a metal–dielectric interface as a bound, non-radiative surface wave, with its field amplitudes decaying exponentially perpen-dicular to the interface. Although photons can be converted into PSPs by means of a plasmon coupler (a grating or a prism in many cases) this 'light' differs considerably from plane electromagneticwaves4. PSPs are characterized by first, a pronounced disper-sion (energy and momentum are not linearly related by the speed of light); and second, a field intensity that is concentrated at the interface and strongly enhanced there. Some of these properties make these modes a sensitive measure of interfaces and ultrathin films. If plasmon surface polariton fields are used to illuminate interfacial structures in light microscopy, high contrast without loss of spatial resolution can be obtained owing to the high sensitivity of the plasmon resonance coupling to (for example) small optical thickness variations of thin dielectric coatings.

Optical chemical sensor based on surface plasmon measurement.

Abstract: A new optical chemical sensor was developed for chemical sensing based on light-excited surface plasmon measurement. Concentration of the chemical species is found in liquid or gas without the help of a reagent but by measuring the resonance condition of the surface plasmon on the sensing metal surface. The resonance condition is given by the dielectric constant of the sample faced on the metal. The developed sensor can be compact and simple, because of the absence of mechanical moving parts, by using multichannel angular light intensity detection with a photodiode array and a Fourier transform optical setup. Experimental results are shown for measurement of ethanol concentration in water. The detection limit for ethanol in water was 10(-4) wt./wt. by the experiments with the developed system.

Optical chemical sensing employing surface plasmon resonance

Abstract: An optical sensor based on the phenomenon of light-excited surface plasmon resonance has been investigated to measure liquid chemical concentrations. A white light source is used to excite surface plasmon waves at a metal/analyte interface. The wavelength of maximum absorption in the reflected light depends uniquely on the refractive index of the analyte.

Desorption stimulated by laser-induced surface-plasmon excitation

Abstract: Atoms with energies of several electronvolts are ejected if small metal particles are illuminated with low-intensity visible laser light. The desorption rate exhibits a resonant behavior with its maximum at \ensuremath{\lambda}=490 nm for particles of 50 nm average radius. The novel process is explained by a mechanism of laser-induced desorption that is based on surface-plasmon excitation.

Long-range surface plasmon electrooptic modulator.

Abstract: An electrooptic modulator based on electrically varying the degree of coupling of a light beam to a long-range surface plasmon excitation is modeled. A specific embodiment of a modulator is shown to be capable of changing its reflectance from 0.00 to 0.84 on the application of 100 V across a 1-μm thick electrooptic film with a second-order susceptibility of 2 × 10−7 esu. The affect that the width of the long-range surface plasmon excitation resonance has on the performance of the modulator is considered. Plane-wave calculations show that decreasing the width of the resonance increases the amount of modulation possible for a given voltage change. More realistic calculations which take into account diffraction of a beam of finite width show that a decrease in resonance width can in some cases degrade device performance.

A Compact Surface Plasmon Resonance Sensor for Measurement of Water in Process

Abstract: An optical sensor based on surface plasmon resonance (SPR) for water measurement in process has been developed. The optical setup of this sensor is made in a simple and compact way, by the use of a laser diode as a point light source, providing an angularly spread (convergent) beam incident to the sensing part with imaging optics. Multichannel detection by a photodiode array and the Fourier transform optical setup eliminates the need for a mechanical angle scanner or a rotary stage in the system, resulting in a reduction in the size, the weight, and the cost of the sensor. Water concentrations in ethanol were measured by this sensor. Water concentrations of from 0.3% to 10% were obtained. Temperature dependence of the sensor and the method for compensation are discussed.

Method and apparatus for detecting low concentrations of (bio)- chemical components in a test medium using surface plasmon resonance

Abstract: A method and an apparatus for detecting low concentrations of at least one (bio-)chemical component present in a test medium in a test cell, having a metal layer as sub wall with an external glass prism, using the surface plasmon resonance effect. A light ray is coupled in and, after attenuated total reflection, is coupled out and the intensity thereof is measured. The incidence angle position of the resonance curve is determined under the influence of the change, caused by the component, in the dielectric constant of the test medium near the metal layer. An adjustable selector is applied to the metal layer, in order to influence the incidence angle position of the resonance curve, through which the concentrations or concentration changes of one or more components in the test medium can be simultanously determined through one or more differential measurements. A preferential association and therefor a higher concentration at the metal layer of one component above another is brought about.

Surface Plasmon Scanning Microscopy

Abstract: The use of surface plasmon resonance measurements for the microscopical imaging of surfaces and thin films has been investigated. Theoretical results are presented for sensitivity optimization and focussed beam measurement. Experimental results are presented for scanned beam and plane-wave imaging of silver surfaces and superimposed dielectric layers. Thickness sensitivity of about 3 angstroms has been achieved, with lateral resolution better than 20 microns.

Surface plasmon interferometry in the visible

Abstract: Plasmon surface polaritons that are launched at an index step from a Ag/dielectric coating/air to a Ag/air interface interfere with the evanescent waves of the driving photon field. The resulting intensity distribution on the Ag surface can be imaged by the recently developed surface plasmon microscopy. We show that it is thus possible to derive the real part as well as the imaginary part of the complex surface plasmon wave vector.

Surface-enhanced resonance Raman spectroscopy of iron(II) and ruthenium(II) bipyridyl complexes adsorbed on silver sols

Abstract: Surface-enhanced resonance Raman scattering (SER RS) is reported for [Fe(bpy)3]2+, [Fe(bpy)2(CN)2], [Febpy(CN)4]2– and [Ru(bpy)3]2+ adsorbed on Ag sols. In each case the enhancement factor is approximately 106, such that even very weak bands have appreciable signal-to-noise ratios, and a detection limit of ca. 10–12 mol dm–3 can be achieved. The band wave-numbers and relative intensities are not significantly different from those of the resonance Raman spectra of the free molecules, indicating that these species are not chemisorbed to the Ag particles. Thus, the enhancement is due solely to surface plasmon resonance, which also leads to quenching of the strong luminescence of the [Ru(bpy)3]2+ ion. The first meaningful SER RS depolarization ratios have been obtained by careful control of the state of aggregation of the Ag sol.

An additional surface plasmon mode of a bare jellium aluminium surface from self-consistent microscopic calculations

Abstract: Using the time-dependent local density functional (TDLDF) theory and analytically continuing the resultant response function into the lower half frequency plane, the authors calculate the dispersion relations and Landau damping of the lightly damped surface plasmon modes of a bare jellium aluminium surface, free of foreign overlayers. For the correctly self-consistent zeroth-order surface electron density profile, they find at least one such mode in addition to the familiar 'monopole' surface plasmon.

Improved assay technique and apparatus therefor

Abstract: A method of assaying for a ligand in a sample which comprises incubating the sample in contact with one surface of an optical structure capable of exhibiting surface plasmon resonance, the said surface having adsorbed thereon or bound thereto, either directly or indirectly, a specific binding partner for the ligand it is desired to detect; irradiating the other surface of the optical structure with radiation of an appropriate wavelength; and analysing the reflected radiation in order to determine whether, and if desired the extent to which and/or rate at which, the surface plasmon resonance characteristics of the optical structure are altered by formation of a complex between the ligand and the specific binding partner. An apparatus for detecting one or more ligands in a sample suitable for use in the method of the invention is also provided.

Wood's anomaly assay technique and kit

Abstract: A method of assaying for a ligand in a sample which includes incubating, simultaneously or in any desired sequence, a) the sample b) a reagent X and c) a reagent Y immobilised on the surface of an optical structure capable of exhibiting surface plasmon resonance, one of reagents X and Y is a specific binding partner to said ligand and the other of reagents X and Y is either a ligand analogue or a specific binding partner to said ligand, reagent X being such, that any formation of a direct or indirect complex between reagents X and Y results in an optical surface having an appreciably enhanced optical thickness as compared to the optical thickness of the optical surface which would prevail in the absence of reagent X, which method includes the step of determining whether and, if desired, the extent to which and/or rate at which the surface plasmon resonance effect exhibited by the optical structure is altered by said complex formation.

Observation of Lateral Displacement of an Optical Beam Enhanced by Surface Plasmon Excitation

Abstract: The lateral shift of a light beam suffering total reflection can be enhanced by the excitation of a surface plasmon wave. A shift of ⋍19 μm was obtained in one total reflection at the surface plasmon resonance. A characteristic double-peak structure was observed in the reflected field as predicted by theory.

The Study of the Mercury Interface Using Surface Plasmon Excitation

Abstract: In this letter we present experimental results on the optical properties of mercury measured by means of the surface plasmon technique. Experiments have been performed on a thick layer of Hg supported on an optically polished Pt base. Our results at the mercury-air interface show–quite convincingly–that the electron density at the surface is larger than in the bulk, as suggested previously from discrepancies observed in the values of the dielectric function of mercury as determined by ellipsometry and normal reflectance and confirmed by surface plasmon excitation at the LiF-Hg interface.

Angular resolved surface‐plasmon loss from Si(111) surfaces

Abstract: The dispersion of plasmon‐loss peaks measured with angle resolved electron energy‐loss spectroscopy gives evidence of increased surface carrier concentration from B‐doped (1015–1016 cm−3) Si(111) surfaces which were Ar sputter cleaned and annealed surfaces at temperatures between 800 and 1250 °C. The plasmon loss dispersion curve (ΔE vs Δk∥) agreed with the calculated plasmon energy and cutoff wave vector for an effective carrier concentration ∼10–50 times greater than the bulk doping density. Annealing at temperatures, T>950 °C reduced the surface plasmon peak presumably by annealing defects, and allowed detection of a surface‐phonon loss peak at 22 to 30 meV probably associated with the adatoms of the 7×7 reconstructed surface.

An optical fibre angular displacement sensor employing the surface plasmon resonance effect

Abstract: A passive angular-displacement sensor with optical fibre links using absorbance wavelength modulation has been demonstrated. A simple prism and thin film is employed which exhibits surface plasmon resonance. Test results cover an 18 degree angular displacement range wih resolution of about 0.5 degree, insertion loss 8dB and temperature sensitivity about 0.01 degrees per °C.